The original post of this thread was about formations, so I am adding an opinion in the context of Yesterday's performance.
We started with 4-4-2 and very early it was clear that it wasn't working. It doesn't mean though that it can never work. It largely depends on personel, and probably opposition formation too.
For instance, the guy they played in front of their back four was getting too much time and space. He was allowed to control that area of the pitch. Formation aside, we needed to put him under a bit of pressure. We did this when Dirk came on, and we switched to what looked from the main stand as 4-3-3. However we did wait until half time for that.
I think that we could have made a formational adjustment without making a substitution to handle this, much earlier in the first half.