I'm sure you've come across similar (if not the exact same) analogies but this came to me yesterday and thought it might be a helpful thinking exercise to share
Imagine you are looking at a computer screen. You have a couple of windows open and are doing some work, nothing pressing but you've got things to do. This computer is your mind.
Suddenly a window pops up out of nowhere in the corner. It's bright red and your eye keeps being drawn towards it. You try to focus on the work you need to do but this window is so red and angry and more importantly, you didn't open it yourself, it just popped up out of nowhere. It's intruding. I'm sure you don't need me to explain what this pop up is a metaphor for!
You click on the [x] to get rid of it, but another window pops up. Again, you click on the [x] to get rid of that one and another appears. Before you know it your whole computer screen is awash with horrible pop ups and you can no longer see what you were working on before. The more you click on these pop ups, the more appear. Turns out this pop up is a computer virus and your screen has been infected.
Little did you know, had you just ignored the pop up, accepted it was a little distracting and you'd prefer it not to be there, your computers anti-virus software would have got rid of it of its own accord.
Your intrusive thoughts are these nasty pop ups. Knowing what you know about the nature of these pop ups (when you click on them they multiply and ultimately infect your computer) it doesn't make sense to click, does it? Don't let them infect your computer, allow them to drift in and out and your computer will stay virus free so you can concentrate on whatever it was you were working on.