Penny and Leonard's relationship was one of The Big Bang Theory's ongoing storylines. Fans were glued to their screens to find out if they would eventually end up together. After years of being on-and-off, friends to lovers, the two eventually got married in season 9.

RELATED: Leonard & Penny's Relationship Timeline In The Big Bang Theory, Season By Season

However, fans couldn't help but wonder why it took them so long to get married in the first place. Once they got engaged, they could have easily gotten married soon after but both characters had excuses. It wasn't until Sheldon started pressing them about their wedding that Leonard and Penny walked down the aisle.

Both Characters Felt They Were Too Different

The Escape Hatch Identification - Penny and Leonard on the couch on TBBT

One of the reasons why Leonard and Penny were scared to get married was because they didn't think they were compatible enough. In "The First Pitch Insufficiency," Sheldon gloats that his relationship with Amy is superior to Leonard and Penny's.

Leonard and Penny didn't think much of the comment until Sheldon suggested they take the same compatibility test he and Amy did. This made Penny nervous and she shut down. It came to be that she didn't think she and Leonard had anything in common and it scared her. Because of their fears surrounding compatibility, they had a longer engagement.

Penny Was Never Fully Certain Of Their Relationship

Penny knows on the window while Leonard and Priya have dinner on TBBT

When Leonard started dating Priya, they became serious very quickly. Penny realized what a great man Leonard was during this time and regretted breaking up with him. She also became envious of Priya.

When Leonard eventually broke up with Priya and got back together with Penny, fans were shocked to see Penny question their relationship. After months of missing him, she suddenly thought they were better off as friends. She ignored these fears and stayed in the relationship but it's hard not to wonder if this kept Penny from getting married sooner.

Did Leonard Sabotage The Relationship?

Leonard eating lunch with Mandy at Caltech on TBBT

When the two finally decided to get married in Las Vegas, Leonard wanted to get everything out in the open before they said "I do." Penny didn't have any skeletons in her closet but he did.

Leonard admitted he cheated on Penny when he was away at sea. Both characters saw this as Leonard sabotaging their relationship, but why? He regretted it and Penny forgave him, but it took her a while to enjoy marriage due to Leonard's wandering eye. Fans still can't get over Leonard's behavior.

They Weren't Comfortable Living Without Sheldon Or Raj

Sheldon and Penny sitting on the couch holding up cards with images in the Big Bang Theory

Sheldon and Leonard had one of the best friendships in TBBT. Even Penny grew to love Sheldon, and the three became happy roommates when Penny started spending nights at their apartment.

RELATED: 10 Quotes That Prove Leonard & Sheldon Have The Best Big Bang Theory Friendship

The idea of Sheldon moving out was exciting but scary for the couple because this meant big changes were happening and they weren't necessarily ready. And while Leonard and Penny were happy to live by themselves when Sheldon moved out, they weren't opposed to Raj moving in when he needed a place to live.

Leonard Didn't Want To Be Penny's Bran Muffin

Leonard proposes to Penny on The Big Bang Theory

The night Leonard and Penny got engaged was an odd one because of her emotional state. She quit her job at the Cheesecake Factory months prior and was focusing on acting, but when that wasn't working out the way she had hoped, she realized all she needed to be happy was Leonard.

However, Leonard couldn't help but feel like Penny was settling for him. Now that she had nothing to lean on, she was telling Leonard that she was ready for a more serious step in their relationship. Leonard couldn't help but feel like an afterthought and wanted to be the Pop-Tart in her life instead of a bran muffin. This train of thought could have stayed with Leonard until they eventually got married.

They Didn't Always Have Great Communication

Leonard invites Penny to Switzerland while sitting on their couch on TBBT

The ongoing trend in Leonard's relationships is that he's afraid of being honest because honesty could lead to his partners breaking up with him. Due to his fear of honesty, his communication skills lack in most relationships. Even though he and Penny were also best friends, there was a lot the two kept from each other.

They both kept their fears of their wedding to themselves. Penny also wasn't honest with him about children, and they made up excuses as to why they weren't married yet. Sadly, once they said "I do," their communication didn't get much better.

Leonard Has Always Been More In Love With Penny Than She Was With Him

Wil Wheaton and Penny bowling in The Big Bang Theory

Although fans loved them, Leonard and Penny's relationship didn't always make sense. Leonard wasn't the kind of guy Penny typically dated. Likewise, Leonard had never dated someone like Penny. As complete opposites, Leonard has always been more in love with Penny than she was with him. He told he loved her for years before she reciprocated.

Although the two were in love when they got engaged, it's hard not to wonder if Penny settled because Leonard was so infatuated with her.

Penny Had Serious Commitment Issues

The Big Bang Theory's 'Tangible Affection Proof' dinner

One of the reasons why Leonard and Penny pushed off their wedding was because Penny had a fear of commitment, which she noted in various episodes. In season 11, Leonard found out Penny was heartbroken over one of their breakups because she loved him but was afraid of commitment.

This fear came up again in season 6 at a Valentine's Day dinner gone wrong when she saw her ex-boyfriend get engaged to the woman he left her for. The two often fought about Penny's fear of permanently being tied down to Leonard.

Their Financial Differences Were Worrisome

Leonard and Penny in her apartment, arguing over money from the car she sold

Fans can agree that Stuart Bloom deserved better in TBBT. It was a sad day when his comic book store burned down and he didn't have the funds to rebuild it. Leonard and co. thought it would be a good idea to help Stuart financially but he realized he had to talk to Penny about it first.

This wasn't the first time the topic of finances came up. Penny had mounds of credit card debt and could barely pay her bills. Leonard did what he could to help her but he also hid money once they did eventually get married. Their worries over finances were always on their minds because when they got married, Penny's debt would soon become Leonard's debt.

Both Were Focused On Careers Instead Of A Wedding

Howard and Leonard working in the lab on The Big Bang Theory

Another reason why Penny and Leonard put their wedding off was that they were both focused on their careers. Penny was absorbed in her desire to be an actress, and Leonard was wrapped up in his job at Caltech (not to mention Sheldon's experiments).

Although these two loved each other, they both wanted their careers to work out more than they wanted to get married.

NEXT: What Are The Main Characters' Jobs In The Big Bang Theory?