Minecraft lag on servers?

Quick question about this, should be pretty easy to answer. On a server I play on, sometimes I jump back several blocks, or when I open chests it takes a long time to open. In that time I can move around, but then I suddenly jump back. I'm sure some of you have seen this before, so do you know if this is a lag problem on my side? My fps are high the while time. Would it be something that optifine fixes?

Definitely lag, you either have too many things on your computer, too many things running or both.

Don't listen to this fool. It's server lag. Server's fault. Or you have bad internet.