15 Best How I Met Your Mother Episodes

"Sometimes hours can feel like minutes, and sometimes a single second can last a lifetime."

Barney and Robin's relationship forms the backbone of the show's later seasons, and as strong and moving as it often was, it didn't get off to the best start. Back in season three, they sleep together and Barney finds himself falling in love with her. They then date in season five before amicably breaking up, and by season seven, things had been building for a while for them to get back together.

Only, they were both in relationships with other people. In a moment of passion, the two sleep together again and plan to tell their partners about their mess-up, only for Barney to realise that he still loves Robin and that he doesn't want it to be a one-time thing. He breaks up with Nora (Nazanin Boniadi), but Robin decides to stay with Kevin (Kal Penn), visibly breaking Barney's heart.

The episode also features a funnier sub-plot that sees Ted and Marshall getting high, but other than that Tick Tick Tick is almost pure drama - sad, moving, and heartbreaking, with one of the toughest episode endings to watch on the show.