Funny, true story.
I have dinner at a friend's house (Paul) the other night. After I leave (with a full set of tools in the back of my truck) one of my other friends (Mark) discovers that his old Toyota Tacoma (I used to have one just like it) won't start.
Mark stays over at Paul's house and starts to work on the truck the next day. Lacking sufficient tools to remove the starter, they go to an auto parts store and buy some tools. Toward the end of the day, they get the part removed and go back to the auto parts store.
Mark: "Can you test this?"
Auto Parts guy: "Yes, certainly, just a moment."
Auto Parts guy: "We have tested it, and it works perfectly."
Mark: "But it won't start my truck."
Auto Parts guy: "Start? This is an alternator, not a starter."
After three days of messing around, they manage to replace the starter and get the truck started.