[jacquesm]

Ok, reword that: 'founders selling a substantial chunk of their stock'.

If it is a relatively small portion then it makes sense as a risk diversification strategy.

[Ntrails]

If I had 10 million dollars worth of stock in my company and was otherwise pretty much poor, you'd see me selling a good 50% regardless of how confident I am in the company.

When people float companies they built and worked at for a long time with little tangible reward it is not unreasonable for them to want to take their money and actually enjoy it.