What is the main reason for the fracture of CNC drill

When using a CNC Straight Shank drilling machine, the drill bit may break. So, what is the cause of the fracture of the CNC drill?
The main reason for the fracture of CNC drill

1. The drill bit becomes dull, but the drilling continues.

2. The spiral groove of the drill bit is blocked by chips, and the chips are not discharged in time.

3. During rapid drilling, the feed amount has not decreased, nor has it been changed to manual feed.

4. The cutting edge of the drill is too sharp, and it will crack, but the tool cannot be retracted quickly.

5. When drilling soft metals such as brass, the back angle of the bit is too large, but the front angle is not smoothed, causing the bit to rotate automatically.