If you are one of those people that can't decide on a champion to main, just like variety, or think it would be cool to play whatever just kicked your tail in lane or what some streamer is playing then I have this observation to make.

Don't make a decision about a champion until you have at least 3 games on them. Realistically you probably need more with a new champion, but even with an old favorite it is probably going to take that long to get accustom to their auto attack animations and their spell rotations again.

On a similar note consider that even on your favorite champions you won't end up with a 100% win rate. Maybe 60% if they are evenly matched in power with the current crop of commonly played champions and fit with the meta of the moment.

Or to put it another way, if you are good with a champion and enjoy playing them and you lose two games on them don't hang them up just yet. Take some time and review your games. Maybe read an updated guide on them or check probuilds.net to see what the pros are doing with them. Mabye attack speed marks are currently better than the magic penetration marks you have been using. Give some consideration to why that might be and try it out in a custom or normals match to see how the changes feel.