Ruby Perf Myths: GC and Concurrency

I've been doing this for a while now, so I've heard lots of guesses as to why Ruby isn't faster. I refuse to say "slow", because Ruby isn't meaningfully slower than it's close competition (exception Javascript, but I would rather say 'JS is fast' than 'Ruby is slow').However, these guesses are usually wrong and rooted in misconceptions. Let's talk about the big three I hear the most often.