#7: It Won't Shift
You pull away from the dock and push the shifter. The boat never leaves idle speed. The shifter is not engaging the transmission.
Solution: If you have e-link electronic controls, it might be a fuse. But, since 90 percent of small boats still use mechanical cable shifts, it's probably a stuck or broken linkage. Start at the gear box to make sure the cable hasn't become detached from the shift lever on the transmission housing. If internal corrosion has caused the cable to stick, try wiggling it free - or if need be, shift manually at the engine/transmission - just don't try any fancy docking maneuvers. If the problem seems to be on the transmission side of the linkage rather than the cable side, it might be an actual transmission failure - there's probably nothing you can do out on the water.
Prevention: The leading cause of transmission failure is lack of fluid or gear oil, so keep those levels topped off and changed as prescribed. Regularly maintain the end fittings and hardware, and periodically service the cable.
Carry Onboard: Extra transmission fluid and wire, tie wraps and J-B Weld for quick linkage repair.