Because most people take it personally when their advice gets ignored—then celebrate when the person fails.
Here's what happens when you say "I told you so":
• You lose all credibility the moment you say it
• They won't come back to you when reality proves you right (pride blocks the lesson)
• Rubbing it in doesn't teach—it just makes you feel superior
• Worst of all, they'll never ask for your guidance when they need it most
If you actually want to help people, give the advice once and show up without judgment when they're ready to hear it.