Is it a necessity...No!
Can plain ol' trail and error get it done...Absolutely!
But as others have said if you're ready to learn, and have a class near by that you would like to take, the cost in time and money could short cut your learning process and assist in getting calls and taking walks earlier than just ol' trial and error.
I learn every time I cook, I learn whenever I'm around others who are cooking, I learn when judging, I learn from competitors at competitions, I learn from lots of forums, and from cook books and other internet sites.
Some of that learning may pay off in competition, some may pay off at other times, but the day I don't learn something, is the day I start to die!
Take what chances and times to learn that you can, if that means a class, then take the class, if it means finding and working with a mentor, then do that too, never refuse the opportunity to gain some additional knowledge!
JM2C!