Are You Wizard Material?

Ask yourself this question: When faced with an opponent is your first instinct or desire to blast them with magical energy?
If you said "Yes" you are not Magic-User material.  You should probably pick a different class.
It sounds like you want to be a superhero.  Nothing wrong with that, but that's not what a Magic-User does.
I may not have said this before, or I may have, but magic is about knowledge, not cool powers.  I realize that might seem counter-intuitive, but it's true.  The whole reason the other classes don't get magic is because magic is extremely powerful and dangerous and should not be used willy-nilly, if at all.  Think of magic as a nuclear weapon.  It is inherently dangerous and hard to control at the best of times.  It's fallout is understood, but not easily controlled or dealt with.  For proof of this I offer you the Owlbear.

It's like Woodsy Owl and Smokey Bear got drunk and screwed.

The Owlbear, a classic monster from Dungeons and Dragons, is, by all accounts, the product of wizard experimentation.

Oh my heavens!  Little girl, run...RUN!

"Owlbears are probably the crossbred creation of a demented wizard; given the lethality of this creation, it is quite likely that the wizard who created them is no longer alive. Owlbears are vicious, ravenous, aggressive, and evil tempered at all times."-AD&D 2e Monstrous Manual

That ain't natural.
But it is badass.
This is the product of magic when it is in the wrong hands.  Now Owlbears breed naturally in the wild and have a lifespan of about 20 years.  This is the unpredictable outcome of magic used for wondrous creations but poorly stewarded afterward.  Just the idea that there are places of "wild magic" suggests that this stuff is too potent to be allowed into the hands of the foolish (fighters) or the self-serving (thieves).  Clerics get to use magic, but their magic is highly regulated by their gods, so that is not too much of a problem.
But Wizards...that is Magic-Users, they are a different story.  The duality is that they covet magic for its own sake and simultaneously know better than to use it.

Ask yourself another question: You are working in your library and it has gotten dark.  A candle is on the table beside your lectern where you are reading a new spellbook.  Do you:
A) Cast light in the room
B) Cast Unseen Servant and have it light the candles
C) Stop reading and light the candle yourself
D) Realize you've been at this all day and stop for a cup of tea/pipe break

If you said A or B, you are not ready for the life of a Magic-User.  Put down the spellbooks and pick another class.
If you said C you have the right mindset for a Magic-User.  You won't waste a spell or magic power for something you could just as easily do yourself.
If you said D you might already be a Wizard.  After all you are supposed to be a Magic-User, that is one that uses magic, not an obsessed power hungry madman.

Remember this one?

Casting LIGHT for the party

Found at THIS LINK?
That's what even the simplest magic is supposed to be like.  That's the effect it should have.
Magic is powerful stuff.  You can use it for fun and profit, sure, but that should not be your first instinct.  Don't waste that Magic Missile when a poke with a stick will do the job!  And be mysterious about it too.  Too many people that WANT to play Magic-Users just SHOULDN'T.  They want to be flashy, showing off their power and resorting to magic first, only to find themselves bereft of power and spells when it is crunch time and they really need it.
Say you don't have a spell for a situation.  Relax, there are options that have worked since time immemorial that did not involve magic.  And don't let the party know that  you don't have a spell.  Play it off with seemingly wise and aloof superiority.
"Can't you cast something?" they will say.
"I could," you coolly reply, "but I won't.  This situation does not call for unleashing forces the human mind is ill-prepared to comprehend.  We brought a thief along for just such mundane tasks."
Yeah, that's how you play it.

If you can do that you might just be Wizard material and one day be able to summon demons from the 666th plane of Hell to the Prime Material Plane to get you a cold beer, but if you survive that long you'll be smart enough to know not to do it.  That's what we have hirelings for.

So what have we learned?
Magic is dangerous and should by no means be allowed in anyone's hands so you, the Magic-User, are the best person to horde it and by no means allow anyone to use it.  It's for their own safety, I assure you.