the uploading stop with !!! in the code

Hello I tried to download my code with "!!!" in a message on a display. It never worked. I thought the card was out of order, but no. The Hazards of C.

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You just add spaces between the ! ! ! The !!! is a signal for the (older) bootloader causing it to jump into programming mode.

I tried to download my code with "!!!" in a message on a display.

Why? What does "!!!" convey that "!" does not?