From Brian McAboy's "The Subtle Trap of Trading", he lists 39 mistakes in trading, which states,

"21. Trading the opinion of others (e.g. market direction)
This one is analogous to the previous mistake, except that now we're
talking about listening to the opinions of others with regards to the
direction of the market.
Remember, everyone has their own perspective. Your indicators and
information may be saying the market is bullish, when you hear someone
else say that they think the market is bearish.
Again, stick to your own information and indicators. It's okay to listen to
others, but filter the information before you act on it. Stick with what
you know."

The so called experts have a right to their opinion. If you ask me, they are more interested i the 'face' of having the right 'guru opinion' because they crave fame or are trying to impress in order to attract 'managed monty', thereby earning commission, management fee etc.

When commodities are rising, guru Jim Rogers will come out on Bloomberg and CNBC espousing his 'correctness' in predicting the commodities boom.
When the markets are tanking due to Eurozone debt concerns, GloomBoomDoom.com merchant Marc Faber will esouse his 'correctness' in prediction the crash in equity markets. More subscriptions to his report and more fees.
When equities tank on some 'event', Mark Mobius will espouse his view that 'buying stocks at good value', in order to get more manged money to earn more management fees for Tembleton...