This one is easy...moisture. Mold MUST have moisture to survive. Take away the moisture problem and prevent the mold.
Probably the single biggest misnomer in remediation...while bleach may kill mild topical mold, it IS NOT effective against most mold. It does not have the contact time required to kill mold.
If conditions are right, mold only needs 24-48 hours to start colonizing. You can have a mold issue before you even know you had the right conditions for mold.
Most customers think that crawl space vents are all their home needs to prevent mold. This is not true. In humid climates like MD, and with more and more water penetration through cinder block, vents alone are not enough. The whole industry is moving towards controlled crawl spaces.
I have heard numerous times that someone's answer to smoke damage smell is to simply paint over it. Nope. Smoke smell will absolutely wick right through latex paint. A smoke cleaner and encapsulant is the only real way to get rid of smoke damage odors.
No. In areas less than 10 sqft, or even a little larger, you can take care of topical mold yourself. Simply scrub the area with soap and water and dry as quickly as possible.