There is a tide in the affairs of men.
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures. (Shakespere)
Using the above quote as an analogy, clearly there is a time to reap and a time to sow.
Buffett said, " Our favourite holding period is forever." Please don't take him too literally. His number 1 rule is not to lose money. But in 2008, he lost billions when he bought Conoco Phillips when oil was over $100.
Even great man can be dead wrong. It's easy to get swept up in a great rally when excitement is immense.
Euphoria is your enemy. Take heed!