The author doesn't seem to realize that he will need to pay income tax on the money that he withdraws, on top of the 10% early withdrawal. This makes the cost of acquiring capital much higher than if he took a loan or an investment. If he has $100k in his 401k, and he withdraws it all in one chunk, he will be left with maybe $45k after 10% penalty and taxes.
The upside is that if he does this properly, ie wait until the next fiscal year, and if he doesn't have any other income income, the taxes he pays might be much less than if he had a regular income.
If all he needs is $40k, if I were him, I would look into alternate methods, like taking out a loan, etc. I've gotten some credit card offers for up to $25k interest fee for about a year (2% transaction fee). If he's this confident he will make money, maybe he should investigate this and if it doesn't take off, he can pay it off with a 401k withdrawal. He would need to figure out at what point he would be making income to pay back this loan, etc.
But straight withdrawing money from the 401k seems like a waste.