Test, Test, TEST!!!
Platinum silicone* is a wonderful, amazing, versatile material. You can cast it in a mold, you can thicken it and build it up over a form, you can thin it to let it flow into a smooth, glass-like surface. It's relatively inert and non-toxic, wonderfully translucent, and a little tends to go a long way.
But aside from being a bit messy it has one major flaw...
No, your silicone is not shy. Silicone is normally comprised of a liquid A part and a liquid B part. When mixed together a chemical reaction occurs which solidifies the viscous fluid into the stretchy, rubbery silicone we know and love. Inhibition then, is when something (usually a foreign chemical in the mix) prevents the proper reaction between the A & B parts and keeps the silicone from solidifying. In other words - a big goopy mess.
The extremely frustrating thing about inhibition is it seems to be caused by extremely random things! Something as simple as wearing latex rubber gloves (latex and silicone are mortal enemies!) while handling and mixing your silicone will cause inhibition.
Which is why it's extremely important to ALWAYS DO A TEST FIRST!
Need to wash off your silicone pieces before painting/adding further detail etc? Test that soap first! Aloe inhibits silicone (see? Told you it was random) and guess what? A lot of soaps have aloe in them.
How do you do a test? While wearing vinyl or nitrile gloves (which don't cause inhibition) wash out a small mixing cup with the soap you are thinking of using. Rinse well. Then mix a small batch of silicone in the cup. It doesn't have to be big at all - less that a teaspoon in total will more than suffice. Leave it for the recommended curing time (which will vary depending on the brand and type of silicone you are using). When you return, give it a poke. Has it solidified? Yes? Great - go ahead and use that soap! No? Then something in the soap is causing inhibition and you need to switch brands.
You need to do a test every time you add an untested substance into your process. Just because one type of soap works doesn't mean all of them will. Ditto with glues, if you are attaching foam pieces together before you coat them in silicone.
T'is a far, FAR better thing to sacrifice a teaspoon or two of silicone then forge on ahead and potentially ruin ALL your expensive silicone and all the time and effort you have put into your piece.
If you learn nothing else about silicone your mantra** should always be - TEST! TEST! TEST!
* This article talks mainly about Platinum-based silicones. Tin-based silicones are less prone to inhibition but have their own unique challenges. ** A mantra which, by the way, will serve you very well for a lot of non-silicone stuff too! Scientist-like habits can lead you to great artistic triumphs!