Succinct means brief and concise, to the point. A succinct argument is one that more directly addresses the point under discussion.
The "traditional" meaning of KISS completely misses the point. The biggest problem KISS addresses is over-complication of plans - and it is not a problem of stupidity. Those most prone to over-complicate are the more intelligent, especially the highly intelligent and highly educated, but lacking in practical experience. Experience, especially wide experience, is the best prophylaxis for over-elaborate plans.
In large-scale planning, especially where the planner cannot see it through to completion or which has too many complications, it is easier to come up with excuses as to why it didn't work out than to actually figure out what caused any problems.
It is human nature to try to explain mistakes away - if you want to get better though you need to avoid situations that make it easy to do. Almost all government projects fall into this group, which is why many who tend towards libertarianism have practical experience and have dealt with the government enough to understand the way it actually works . (Former police, former military, and engineers, for example, tend to be over-represented among libertarians (in my reading and experience anyway, I haven't seen any really reliable statistics)).