Why you should not touch your halogen Bulb with your fingers when replacing it.

Fun fact:

You should not touch the surface of a quartz halogen bulb with bare fingers. The quartz surface will be exposed to the salts and oils in the hand. 

This will cause a weak area and lead to premature lamp failure. 

If you happen to contact the bulb with your fingers, carefully clean the quartz surface with a gentle solvent such as alcohol.