He's choosing to compare the two sets of possible events, set a) "the actual events" and set b) "the events had we not invested in January". You could call set c) "the events had we invested in the summer" and add that to the discussion, but they are far away from the actual events as to be deemed irrelevant to the discussion. How far back shall we take the possible permutations?
Basically, he's dealing with the hear and now and the January decisions are what counts. They would have planned for the summer without January's expenditure, so it is relevant to discuss it.