I played professionally for a number of years. A lot of Internet and live. I also have a large number of friends from the scene as well.
That's fine if you believe that, but it is possible to be a winning live player and not use tells. Tells being used are more anecdotes than typical situations that come up.
At live poker, the number of hands ranges from 15 to 30 per hour. Most hands don't go to showdown, so you simply never get the information you need. Unless you are playing higher stakes with a smaller player pool, or a small home game, you may not have the same opponent at your table for a long time even if they're a regular.
Giving off tells assumes that opponents are perceptive enough to notice, or naive enough to fall for overly obviously tells. This is asking too much for a lot of weaker opponents. And most people won't be involved in the hand and paying attention.
The most useful "tells" may not even qualify as such. They're usually weak or bad players trying their hand at bad acting in a way that tends to be obvious after you've played enough.
You also run into the problem that even amateurs can familiarize themselves with tells and try giving off "reverse tells" which reduces it to a game of "leveling".
Most of the time the best decision is irrelevant of whatever behavior an opponent is perceived to be exhibiting. If I'm following through on a bluff against an opponent on a flush draw (comes 35% of the time if they see the turn and river), and their draw comes in and they sigh "guess I'm beat" and shove into me on the river, I can't call with ten-high.