Now the rest of the story; "but only after you have done 10" So what was the goal to be accomplished here? The feel aspect of speed training is one you'll be hard pressed to find a good physiological study on yet it is a key item of the Lydiard system.
Wednesday's workout for Mike was based on how well his steady state had moved up over the last few weeks. The goal was to move it up more and based on his recovery (Axiom #2 How well you recover is a better indicator of your condition that the workout itself) he did himself a world of good by getting to 10.
But how do you know when to push and when to quit?
This is where reading how you feel is important. In running a hard volume speed workout like the 10 X 1000 repeats (or 20 X 400, 10 X 800, or 6 X 2000) the goal is to work hard and long, to produce a large volume of lactate so that the all the mitochondria in all the fibers get good at soaking it up and using it as fuel. Much like a funnel there is only a certain rate that the lactate can flow into the mitochondria before it over flows and then have it show up in your bloodstream. The mitochondria can get very good at using lactate but it does no good to over fill the funnel (running too fast too soon). It also does no good if the workout is too short and they don't have much processing of lactate to do. You have to feed them at the right rate for a long time to get them good at processing lactate.
Mike needed to work hard to get to all the fibers but that had to be balance with the right rate so it was not just dumping it into his bloodstream. This is why the goal of ten and the holding back for the first three. The actual times were of a less of a concern, the volume of work at the right rate (which would allow him to get to ten) were the goals.
It is a balancing act but an important one if you want to realize your potential.