Hey guys. I recently finished "Set for Life" and in it the author suggests keeping your investment savings (not your emergency savings) in the stock market so you can ride the general upward slope of the economy before you utilize it. This makes a kind of sense, but I have concerns.

And it's not as though I am terribly risk adverse, either. I have a separate portfolio of stocks which are all highly aggressive, but my timeline for those is decades in the future. 

Basically, because my estimated timeline before purchase is 12-36 months then that isn't very long term and thus I wouldn't be riding the "general upward slope of the economy" but would rather be subject to whatever short term market conditions come my way. 

What do you guys think? If you were going to be making a purchase in the next 3 years would you keep your money safely "under the mattress" in the bank, or would you place it in the market and accept the risk for the possibly great rewards?