There are also psychologists who lived happily ever after. Does this make their advice worthy? In my opinion, it is more important whether YOU will become happier from such advice.
In antiquity there was such a principle: if you observe your teaching and do not drown, then the teaching is fair. This is, of course, about philosophy. In other sciences, everything is somewhat different. It is not always possible even to implement your ideas. A famous example is the comet predicted by Edmund Halley. He calculated quite accurately the date of the appearance of the comet in the sky, only he did not have the opportunity to live up to this moment. Does this mean that he was wrong? By no means - everything has come true.
Now closer to psychology. A. Maslow considered the need to love and be loved as one of the levels of the hierarchy of needs. When he proposed to his beloved, he was not at all sure that everything would work out. He understood that he needed reciprocity for happiness, but this understanding alone was not enough! And if the marriage did not take place, this would in no way destroy Maslow's theory. And that would not mean that a person does not need love.
P.S. The Maslow couple lived happily ever after.
And what, apart from Internet memes, is the assertion based on that their lives ended tragically? Both died of natural causes at a respectable age: Benjamin Spock at 94, Dale Carnegie did not live to see 67 (by the standards of 1955, normal, and lymphoma does not spare the happiest and most successful people). It is not true that Spock died in a nursing home (and even if it were, in America, as far as I understand, this is treated more calmly than in Russia). However, it is known that he had financial problems in connection with paying for medical expenses - well, he seems to be not an "investment guru", but on another part. The fact that "Dale Carnegie died all alone" is also doubtful, given the fact that at the time of his death his wife was engaged in publishing, and they had a four-year-old daughter. Also the very next day, his obituary was in the New York Times, which indicates a high public interest in the deceased (http://www.nytimes.com/learning/general/onthisday/bday/1124.html)
In general, check the facts.
If the advice of a person who by some coincidence is called a psychologist is disgusting, then they should not be used at all. You can also print his portrait, hang it next to the portraits of famous psychologists and throw darts at them :)