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Getting started in stock with one special field of activity
I don't think investing in only one industry, which you may know well, is very wise. You may want to invest in that industry but you should not restrict yourself from investing solely in that industry.  There are many times when your chosen industry may not be performing very well and other industries are performing much better. If you restrict yourself to just one industry you may be either out of the market for long periods of time or your portfolio may show negative returns for extended periods of time. You may want to know an industry or a number of companies very well but do not fall in love with them. The worst thing you can do is get emotional about an investment, an investment is there to make you money not for you to get emotional about. Don't restrict yourself, instead look to maximise your returns with investments that are performing better at the time.