It doesn't take much to get off the track. Especially the stronger the routine the easier it is to derail. As long as you let that small thing interrupt you.
So it's better to ignore everything else as far as possible until you are through your routines. Else, it might be hard to get back. Those routines are usually there exactly because they are the hardest things to make ad hoc. You really depend on the routine to get it done.
Take for example my morning writing. If I don't get my trigger sitting on the train I most often skip the writing all the way until the last moment, to my backup trigger. That simple thing works almost every time. No matter what, I step into the train, find a spot, sit down and start to write.
Sometimes the circumstances might prevent part of that happening. It might be so that the train is full, there is no room to sit down. It's hard to write standing, I have tried. And allowed myself to exempt from writing on those situations.
But there are also those preventable interruptions. The things that are up to me. For example those notorious message notifications that keep bugging you until you acknowledge them.