Does everything happen for a sufficient reason?

When every sort of things happen in the natural world, some people think they happen for a sufficient reason, while others argue is a matter of probability. is Is there some kind of grand design to the world? Are all facts determined by physics?

Pro

 * As our investigation of biological and planetary sciences deepens, we learn more about how the world´s systems are connected and events are dependent upon one another. Events which seem "random" are not in fact sheer chance but happen as a part of a chain of causal events.
 * Causality is a natural law, so everything that happens has a cause, and therefore a reason.
 * Claiming that causality is a natural law doesn't make it so. This argument just re-states the principle of sufficient reason without explaining how it is true.
 * Accepting that some events have no sufficient reason leads to a stop in the search for one. Then, if we're mistaken in our judgment of there not being a sufficient reason, we will never find out. Therefore, for methodological reasons, we must accept the principle of sufficient reason.
 * As per arguments against, we have good scientific reasons to believe some events are genuinely random. We may accept that some things may be truly random without giving up on search for causes. There is no methodological dictum forcing us to accept something that we strongly suspect is untrue.

Con

 * What is the sufficient reason behind the precise moment at which a particular atom in a radioactive compound decays? According to our best confirmed science today, some processes, such as radioactive decay, are inherently random at the atomic level. A sufficient reason as to why that atom decayed when it did cannot be given even in principle.
 * The principle of sufficient reason states that everything must have a reason or a cause, not that we must know that reason. Science may not have found the reason yet, but this doesn't put a sound counterargument to the principle.
 * The principle of sufficient reason needs to be empirically proven if you want to use it. Immanuel Kant and Arthur Schopenhauer have proposed proofs of this principle but their proofs are not universally agreed upon and rely upon various assumptions that not everybody agrees on.
 * According to quantum mechanics, some events occur randomly.
 * The probabilities in quantum mechanics describe what happens, but just because probabilities can be applied there isn't necessarily an absence of cause. The cause could simply be unknown as of yet.
 * That is an argument from ignorance, a logical fallacy.
 * Although we can sometimes explain the material causes of tragedy or suffering, that doesn't mean they are sufficient or that they should happen.
 * Errors of judgement are inevitable, and we are always fine-tuning our perception of right and wrong following assessments of cause and effect. Should mistakes happen? Arguably this is how we learn the best: we do "wrong" unto ourselves and others, we observe the effects, we exercise the invaluable fruits of trial and error to align with our highest potential. One man's loss is another's gain, and not all losses and gains are measured materially.
 * There's no known or likely reason for the Universe to exist. But if there's no sufficient reason for the Universe to exist, then everything it contains ultimately doesn't have a sufficient reason either. Therefore, nothing at all happens for a sufficient reason, which trivially implies that not everything happens for a sufficient reason.