Robustness is how much something can break before it is useless. That you are able to understand me at all, is a testament to the robustness of the English language, as I make a lot of mistakes, grammatical, spelling, punctuation, stylistic errors and so on.
In my experience studying Russian and on a few occasions trying to help foreign speakers learn English, I’ve discovered the “word soup” phenomena. If you have a reasonably large vocabulary, you can screw up a lot before you are completely unintelligible. In particular, you can pick out three words and guess what is going on.
For example, “A airplane pilot quickly flew and the” has flying, a pilot, an airplane. It doesn’t matter if you use SOV, SVO, OVS. These elements only make sense in one way. The sentence “The pilot flew the airplane” is extremely robust to errors in grammar. Fine distinctions are not robust to errors in grammar of course.
Now back to toki pona. I’m still a beginner and a lot of the texts I find on the internet are those of beginners as well. A lot of them are utterly unintelligible. It does not take much noise for a sentence to be reduced to unintelligibility.
Robustness can be improved by being wordy, repetitive, and not trying to accomplish too much in any one sentence. In fact, the previous sentence would probably take a dozen or two toki pona sentence to translate without significant loss of meaning. It would probably take double that again to become robust against being misunderstood.
mi pona e ijo. I improve it.
ijo pona mi li e. My good thing + out of place particles.
jan pi tomo tawa kon li pali e tomo tawa kon. The pilot flies the plane.
e jan pali tawa kon tomo li kon tawa tomo. out of place particle + person worker go air container-for-people is airing go container-for-people,
In other words, similar jumbling of the same sentence in toki pona yields complete gibberish.
Don’t get me wrong, I’m not saying this demonstrates that toki pona is broken. If anything, it illustrates that toki pona is the language that is easy to start, but gets harder the more you want to do with it. I also suspect that if I ever became fluent, it would take just as much energy to gain fluency in tp as it would be to gain fluency in any other natural language.