I’ll try my best. For example word “fićfirić”. When you pronounce it it sounds soft and just kinda “rolls over” your tongue. Imagine it being “fičfirič”, it’s very hard to pronounce. Kajkavski may only have “č” but kajkavian speakers can differentiate it when speaking standard Croatian, at least the ones I know can. Even if they can’t majority of Croatians are štokavci and they can differentiate it pretty well. 

P.S. Of course it sounds forced if you force it, you don’t have to tho.