This is a strange (Keynesian) statement, isn't it ?
Investing means to give up consumption in order to use resources to make capital (that is, means of production).  Indeed, certain resources available could be used to consume, OR they could be used to make capital, but not both.  They could also be wasted of course, but what is impossible is to consume and make capital with the same resource.  If you want to "consume time" (that is, if you want to have free time), you cannot use that time simultaneously to produce labor.  If you want to consume electricity for playing a video game, you cannot use that same electricity to make a machine that will build a car for instance.  You can only use a resource once, and it can be 1) wasted, 2) consumed 3) invested (that is, turned into a capital good).

There's no way in which "printing money" can invent resources that can be turned into capital, without not having them consumed or wasted.  This is why "printing money" or any other Keynesian technique doesn't really work in the long run: because resources cannot be double-spend in consumption AND in capital.
Of course, what printing money can do, is to take away resources from some and give them to others.  Whether that transfer of resources improves the economical structure or not is an open debate.  Usually, if the one spending has no choice over on what it is spend, and if the one receiving didn't have to earn it, wasting resources is probable, so usually, taking away resources from some, to give it "for free" to others is wasteful (because you are usually more careful with resources you had to earn, than with things received "for free" and taken from others).

Ideally, the decision not to consume, but to invest, is what is called "saving" and happens ideally with a "sound money" (that is, money that doesn't inflate its basis).  Then, the balance is clear: people earning money (in return for produced value) who do not want to consume this, put the money aside as a saving, and this can be lend out to people wanting to invest.  With sound money, the amount not spend on consumption is then equal to what is available for investment, as it should be.  The interest paid on the borrowed money is then ideally equal to the value of the capital in the new production and is the incentive for the saver to save. 
All printing of money is distorting these balances.