This highly agonizing, emotionally devastating scenario is universally known in the poker community as a "bad beat."

Mastering the psychology of the bad beat is arguably vastly more important than memorizing complex pre-flop raising charts.
Understanding the Reality of Variance
If you get your money in the middle as an 80% favorite, you must accept that the terrible opponent will absolutely win the hand exactly 20% of the time.

If you consistently make mathematically correct decisions, the variance will absolutely, inevitably smooth out over the course of tens of thousands of hands, resulting in massive long-term profit.
Professional players celebrate bad opponents; if bad players never hit lucky cards, they would quit playing poker entirelyThe bad beat is the exact mechanism that keeps terrible, highly profitable players coming back to the casinoYou must separate your decision-making process completely from the actual financial result of the hand Recognizing the Signs of Tilt
A player on tilt completely abandons logic and mathematics, playing far too many weak hands and making massive, aggressive bluffs in a desperate attempt to win their money back quickly.

If your heart is racing, you are angry at the dealer, or you feel an overwhelming, desperate urge to play the very next hand aggressively, you are officially on tilt.
When to Walk Away from the Table
If you suffer a horrific, multi-thousand dollar bad beat, the absolute worst thing you can possibly do is immediately deal yourself into the next hand.

Do not return to the casino floor until the intense emotional anger has completely subsided and you can view the bad beat as a purely mathematical inevitability.
Player ActionThe Mathematical RealityThe Proper ReactionOpponent hits a 2-outer (5%)Expected to happen 1 in 20 timesAccept the math, do not complainPlayer goes on "Tilt"House edge/Opponent edge increases massivelyLeave the casino immediately to reset
Embrace the math, celebrate the terrible decisions of your opponents, and always have the discipline to walk away when the tilt begins to set in.