How do I carry?

Put simply, how do you carry a game? Any tips for this? I like to say I do well at all lanes- but the ones I tell everyone I main are Mid, Support, and Top. It seems like almost every game I'll do well against my lane opponent; at the worst I hold my own, at the best I crush them- and then it comes time for the team to fight together and it all just goes to hell almost every time.

I'm not fatheaded enough to say it's always my team's fault and not mine, nor do I have such a large ego to say I never lose lane (because it happens, just not normally and most of the time it's a jungler who turns it- not the laner themselves) but it does seem to be the case far more often than not that I'll do well and then nothing goes right past 10 minutes or so.

I mean, I perform my role to the best of my abilities. Tank? Initiate, CC, then peel. Mage? Stand back, dish out damage from a distance ADC? Similar to Mage, but with much more positioning plus a Support. Support? Initiate or peel depending on who it is.

I just don't get it, am I unlucky with team members? I'm so tired of doing well in game and having nothing to show for it but a stream of defeats.