system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Can some one please explain me why are winglets required in planes and why dont Fighter planes have them ?
gpt
On a plane wing there is a low pressure on the upside and a high pressure on the downside. This pressure differential is basically what makes the plane fly. 
Since pressure differentials always want to equalize the high pressure will slip around the tip of the wing, raising the pressure on the upside there and destroy a part of your lift. 

The winglet is there to reduce this.