Why are you bad at scout in Team Fortress 2

Here's a few tips to keep in mind when playing as a Scout:
- Jump and move when attacking. Scouts are much faster than other classes, and by jumping around the enemy, he will be confused and miss.
- Know your map. You need to know where health packs are when playing scout. You'll lose health quickly, so know your escape route.
- Don't run straight forward to "strong" classes. Try to ambush them. If you encounter a heavy, don't run directly to him. Try to be more stealthy until he detects you. Then, run around him while shooting to dodge bullets. Remember, scout has 125 HP (Hit-Points), Heavy has 300.