Unfortunately, such people may one day use such unfair evaluations to deprive this person of a job he might otherwise do excellently.
PEOPLE WILL JUDGE YOU ON THINGS THAT MAY SEEM TRIVIAL,
Sadly good spelling, grammar, vocabulary and (possibly) even punctuation are important, they are your passports into the white-collar professional world of well paid jobs where you won't have to work all hours just to feed yourself or give up your guitar mania. The whole "**** it, I'm going to be a rock star" attitude won't help you get anywhere. I nearly quit my education with such a goal in mind and I'm very glad I didn't. Guitar can only be a profession for a small minority of individuals. Some people will never make simply because they are BRILLIANT musicians and people don't understand their music and they won't compromise. For most of guitar will only be a hobby but it will be a priceless asset to the expression of one's emotions. So, guitar probably won't earn you money but being able to spell and having a reasonable vocabulary might.
IMPRESS YOURSELF AND DEAL WITH IT
If you want to sort out your spelling and grammar you should use a spell-checker like the one you get in Word. They can automatically underline misspellings and grammatically faulty phrases so you spot your mistakes as you make them. This saves you having a tedious job to do when you're nearly finished. If you want to improve your vocabulary then use a thesaurus and try to avoid using the same word twice in one sentence unless it's a pissy one like "a" or "to" or if it just can't be helped (and commonly it can't). "Dudes" for instance are smooth, poised, cool, urbane, sophisticated, decorous etc.
It's important to adopt the right psychology, think of it as a way of demonstrating your strength of will and as an exercise to improve your memory (which benefits from the effort) and NOT as an admission that you are at fault. To tackle and defeat problems which used to be major issues is a sure way of building self-esteem in all areas, and is much better (though harder) than just doing things you find easy. But go really easy on yourself, the trick is to practice and observe but to avoid negative emotions that actually reduce a person's learning capacity. A person's learning ability increases with practice, it's a fact known to any teacher or psychologist. Most people fall seriously short of their potentials because they are too lazy or give in too easily. Frustration frustrates learning. Stay cool, stylish, urbane. blah blah..
This is your mission should you choose to accept it..
Cue credits, groovy music and people with exploding briefcases.
If I couldn't laugh at myself how could I laugh at someone less ridiculous?