Do I really need to wear the retainer?

you spent $5000 on braces (or your parents did). That will be flushed down the toilet if you don't wear your retainer. Your teeth will move back and it won't take long for that to happen. You must wear your retainer and once you get used to it you won't lisp anymore but it takes time. You really wasted someones time and money if you got braces and don't wear your retainer you would have been better off spending the money on something else. If you just wear it at night your teeth will move during the day and it will not fit properly at night which will make it hurt and pretty soon you won't wear it at night either. Then when you don't wear it at night your teeth will move to the point that even if you wanted to wear it you wouldn't be able to get it in at all