system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why we have two types of screw heads/drivers?

While putting together a piece of furniture recently, I constantly had to switch back and for between a Phillips head screwdriver and a flat head screwdriver. Why do we have two types and not just one. If we could have just one, wouldn't the Phillips be the best?
gpt
Flat heads are easy to use by humans, they have 2 downsides.  The first is that the bit slips horizontally and falls out of the screw.  They tend not to strip very easily, both bits and screws are simple so they are cheap to manufacture

Phillips heads exist because the flat head does very poorly when you have a machine turning the screws.  These machines tend to be very powerful and the flat head screws would get over tightened and break.  So the Phillips was designed so that the bit would slip out if it reached that point.  The down side is that this "feature" works fairly shitty when it's a human doing the work by hand or using a low power consumer drill. 

tl;dr The bits exist for different applications.