For those who need something short but sweet...

"What's the most complicated thing in the universe? The hardest problem to solve? The toughest riddle to crack? The most challenging task to fulfill?"

The quartet stared at the guard, each having different expressions on their faces. The Doctor was already deep in thought, brows furrowed, seeming to debate on which answer he had in his mind was correct. Amy and Rory shared a look, both turning to face each other at the same time. Rory had almost no clue as to what was happening until he looked into Amy's eyes. Amy seemed to have told him the answer through it. (Y/N) glanced at the Doctor, then at the couple, back at the guard, and back at the Doctor, whose eyes were shut. Being the youngest and least experienced, they had absolutely no idea what the answer to the question was. The redhead cleared her throat.

"Is it love?" She looked back at Rory, who backed her up instantly.

"Y-yeah. Love is pretty complicated. There's no fixed instruction to how it works, how it's done and what the outcome is. It needs to work out within the two, and depends on how connected they feel," He shrugged, satisfied with his elaboration.

"Wait till you see my work,"(Y/N) muttered, but it was audible to the couple, who gave them a stare. They ignored their eye contact and glued their eyes to the floor.

"Sorry, love," The Doctor finally spoke and having heard the 'latest human he picked up', eyes sparkling as he had finalized an answer. He ruffled (Y/N)'s hair, who annoying slapped his hand away, before turning to face the guard.

"It's love. What the couple said, but not completely."

The guard straightened up, awaiting an answer he may have not heard before. The Timelord grinned from ear to ear.

"The hardest thing to do is finding someone," He said, "Someone who will always be there for you."

Rory opened his mouth to argue that he and Amy's answer were similar, but he continued without giving him the chance to do so.

"Someone who understands your pain and sorrow, your happiness and joy, your way of life, and that someone may not love you in a romantic way. It could be a platonic relationship, no less. It doesn't need to be of an opposite gender or different species. It doesn't need to be someone who's 20 years younger or 20 years older. That someone should know that it isn't the time spent together or mutual exchanges that matter. It's the connection you feel with that someone."

He paused briefly to catch a glimpse of Rory, snapping his fingers and pointing it to him, "Yes, Rory, you're right."

The man immediately put on his infamous 'I don't know what's happening so let's go with the flow' face, nodding slowly.

"Despite the fact that both of you are far apart, in different countries, galaxies, universes, or even dimensions, that person will always come back. That person will accept you for who you are, acknowledge your wrongdoings and forgive you for them eventually. That someone may not know you best, but knows what's best for you."

"And most importantly," The Doctor turned to (Y/N), giving them a smile which warmed their heart, "That someone ultimately never leaves your side, no matter how long you've been apart."