PSA: Don't rush a damage item if you're losing lane

Seriously, just don't. I don't care if you're a snowbally champ that needs kills, the fact that you're losing lane invalidates any chance of you snowballing from that point forward. The only way you will be useful is if you can live long enough to contribute, and damage items will not let you do that. If you're a Riven, build Titanic Hydra and Deadmans, not Ravenous Hydra and Ghostblade. If you're GP, don't get Triforce, get Iceborn. If you're Vlad, don't upgrade Gunblade into WOTA, get Spirit Visage instead.

Think of it this way: if you're losing lane, that means your lane opponent is winning lane. Naturally, they will go straight for their main damage item first. If you, as the loser, go straight for a damage item first it will NOT cause you to out-duel them because they could already out-duel you pre-first item. To put it another way, think about two people standing side-by-side. One of them takes 2 steps forward (the winner of the lane). The other takes 1 step forward (the loser of the lane). From that point on if you both keep taking 2 steps forward, the other guy will always be ahead of you because of that early lead.

Note that this only applies to lane phase, and does not take into account jungler interference. When I say "losing lane" I'm talking about if you die more than 3 times by ~8 minutes and/or are severely behind in farm. The best thing you can do for your team if you lose lane is to go tanky and get a damage item later on if necessary. This does not just apply to top lane either. As a mid laner, instead of rushing an Athenes or Morello for mana regen/CDR, get a Rod of Ages or Zhonyas or Abyssal Scepter. RoA is actually an amazing item on a lot of currently popular mid laners (e.g. Malz, Brand, Anivia, or even bursty types like Ahri or Viktor).

So stop holding your team, and yourself, back by building straight damage. Going tanky will not only help you survive into the mid-game better, where you might make a comeback, but also stop you from dying less and causing the opposing laner to snowball uncontrollably.