Listen carefully the next time you debate religion or politics. People prefer using the word logic over reason because it makes them sound more correct. Logic is provable, valid reasoning: a way to remove the human mind from the equation and produce a repeatable result. But subjects such as religion and politics are creations of the human mind: you cannot remove it. Other subjects like the history of Earth or the universe are beyond the reaches of logic because they involve complex interactions over millions of years. Proving the result of such long-term experiments would require a computer inconceivably more powerful than any we have today.
Avoid implying an external truth by replacing "logical" with "reasonable" and "illogical" with "unreasonable" in discussions not dealing with computers or mathematics. The debates will then focus less on causality and more on likelihood. "A is more likely" not "A is correct".
Realize claims what follows is an external truth, but it's probably conjecture. A truth wouldn't need to prop itself on this phrase. Instead of claiming fact, just explain why this reason carries more weight than the others.
"What you have to understand is that …" and "What you have to remember is that …" are similar but slightly less condescending.
Facebook vaulted it's complicated into our pop culture lexicon. Beyond saying you are a relationship train wreck, it dissolves your responsibility for the situation. "It" implies a thing outside of you, while your relationships are half of you. But "we're complicated" is just half way there.
Rocket science is complicated because it involves hundreds of thousands of parts placed meticulously together (a rocket) in order to move safely through space. Though the human brain is also complicated, people are not complicated. They are merely confused and confusing to others. Instead of imagining an external complication, try clearing up some of the confusion. It makes everything much simpler.