1. In the first year or two, while you are still learning to invest, it's much safer to operate on a cash basis.
2. Generally margin buying should be done by younger investors who are still working. Their risk is somewhat less because they have more time to prepare for retirement.
3. The best time to use margin is usually during the first two years of a few bull market. Once you recognize a new bear market, you should get off margin immediately and raise as much cash as possible.
4. If a stock in your margin account collapses in value to a point where your stockbroker asks you to put up money or sell stock, don't put up money, think about selling stocks.
O'Neil also said "All of this depends upon the current market situation and your level of experience. I have always used margin and believe it offers a real advantage to an experienced investor who knows how to confine his or her buying to quality market leaders and who has the discipline and common sense to always cut losses short with no exceptions."
These are general rules. Everyone's situation and every stock is different. I think there is a decent chance for TSLA to rally higher from 180, definitely I'm not suggesting people to close positions with a big loss then watch the stock to fly. I just hope people understand what's right what's wrong regarding using margin, so they don't get hurt down the road.