Blush!
Please let me clarify: the only thing I AM an expert on is beginner mistakes! I may have missed one or two, but I think I'm intimately familiar with mistakes that can be made, and even some that few manage to commit.
For example, forgetting that water runs downhill, but then STOPS if it can;t go any further. that mistake started my obsession with drainage ditches.
And I started gardening right during the worst two years for sugs in Western WA for decades! Excuse me, it was a GREAT two years if you happend to be a slug. I would wonder "where did all my seedlings go?" until someone explained what the slime trawils meant.
Here's a backwards beginner mistake: "everyone" said it would be a big struggle to get any tomatoes to ripen where I live. Finally I could n;t keep three plants from fopllowing me home from a nursery. Even the lady who sold them to me rolled her eyes and bit her lip as if to say: "YOU'RE quite the optimistic gardener, AREN'T you?"
I carried them inside and outdoors each day for weeks until nights stayed over 50 F. I figured it was just for practice, to see what they looked like as they struggled to ripen.
Well, one of the three did give up and fade away that very-cool spring and summer. As I expected (Supersweet 100".
But the other two eventually got around to fruiting and even ripening several per day! And they tasted great until late summer when it got too cold again.
Beginner mistake # 1 is probably "not acting on good advice".
But beginner mistake #99 is "believing everything you hear".