You got five very good answers above my own one. I will not repeat all in my own words, but I add this:
Muay Thay is a fighting art, not always focused on tournament-sports.
Original US Kickboxing is precisely that, a tournament-sport with rules like no hitting the back, only hit above the belt (waist-level) and so forth.
Self-Defense depends a great lot on your teacher (from life itself to dollar-grabbing brutes and poseurs), the specific situation, and the kind of attacker or attackers.
But technically Muay Thai teaches more, and trains tougher pupils. Like already mentioned above the clinching/grappling of Muay Thai is a precious skill. Except, of course, against a skilled knife-fighter, than it turns suicidal, as plenty of paramedics can teach you in gory detail.
Personally I was a bum, when I had my own first street-sparring against MMA (Mixed Martial Arts). I would have lost my arm, shattered break, because I was surprised once. After that only the brutality of my own kicks forced me to hold back, but Muay Thai clinching could suffice to counter, shake-off, and outmatch MMA.
Still such is brawling. Real self-defense is usually against real criminals or real combat doggies or real Islamist or Racist extremist/insurgent types who come to cripple or kill. More than awareness such needs the courage to stay calm and keep thinking, as otherwise only a brute could hope to win by toughness alone.
Nowadays documentations like these may inspire you:
Krav Maga Street unlike Dojo
Threat Level of skilled knife attacks:
Knife Attacks, a fiercer realism shown