sdtom, that advice is good for the whole world of philately, and many other human activities.
Can't we say, as well: "yes, start being a stamp collector/philatelist, but don't expect to make money; only the pros/stamp dealers can really make enough money to make a living out of it"? Even they have a hard time now...
However, some implications and interpretations of what you said are debatable.

You imply that "only the pros" make money from something. But isn't it true that money, more or less, is being "made by all kinds of people (the majority of mankind), in various activities, even if they are not necessarily "pro(fessional)s" in that field?
I agree, of course, that the pros/experts (in any field) are the most knowledgeable, by definition, and they have the greatest chance of being successful, including at investing/making money.
For most of us, philately (including the designing of personalized stamps) is just a hobby, and we spend more than what we gain, overall.
