It is only undeterministic until it is observed. We can observe such periodicty as it related to our lives, consciousness, and of course the market. Einstien had the same worries about QM as you do.
[...How can one "accept" such an undeterministic theory as Quantum Mechanics?...] Surely you're joking, Mr. Hed? <g>
As complex and weird as they are, these equations are much better in their predictive capabilities, even if they are only probabilities, than any set of TA rules, no?