Say that you'd like to work on two projects - A and B. Atleast one of them needs to succeed or you'll go bankrupt(or something). Now, most people will probably think that if they divide their attention between both projects, they have a higher chance of bringing in some money. The thinking here is "Even if A doesn't take off, B might still bring in some money". So, B is the cushion against failure of A (or vice-versa). But this plan lacks focus - You cannot fully focus on A or B. Removing either improves focus but it also removes the cushion.

That's what he means by getting "scared".