Take every day probability estimates.
What is the probability that one will be killed crossing this road?
One can have a compilation of all deaths at crossings, maybe even fitted to a functional form, and sees that the probabiliy is 1/10000 that one will be dead after crossing the road.
This does not mean that one is 1/10.000 dead and 9.999/10.0 alive. The probability function is not describing any particular person. When a death occurs, one does not say : the probability function collapsed for this person. In a similar way, the probabilities given by solutions of quantum mechanical equations are just that. A probability . When a measurement happens the quantum mechanical functions that will describe the future probability behavior of the particle change. That is the only meaning of collapse, nothing esoteric. Similar to some polls taken when, once you have taken them the sample you belong to changes, due to the knowledge you acquired from the polling questions and you no longer belong to the polling sample.
So far so good.
Now lets tackle decoherence.
Take a large crystal, you would think it is a classical object since you are holding it in your hand, but you will be wrong. A crystal is one of the clearest manifestations of the underlying quantum mechanical layer of nature. One can measure its symmetries in various ways non destructively, with x-rays for example. Those symmetries are the collective manifestation of the phases that are characteristic of the underlying quantum mechanical nature, each small crystal unit building coherently on each other to grow into a large observable crystal retaining the phases between the molecules and atoms.
The coherence can easily be lost. Take a large hammer and beat the crystal to dust ( do not do it on a diamond, salt is fine). What is the difference between the crystal state and the dust state? The mass and atoms are the same, but the phases were lost, decohered.
In a similar way, all matter starts from atoms and molecules with quite definite phases to each other but generally these phases are lost very fast and decoherence means that even though in principle we might know how one water molecule relates quantum mechanically to a water molecule one centimeter away the complexity of the problem is such that the problem becomes statistical, with quantum statistical mechanics to start with and at large scales with classical statistical mechanics with its classical probability distributions answering questions about matter. It is only in special cases as in crystals, superconductivity, superfluidity that the underlying quantum phases are built up instead of turning into an incoherent mass.
Whatever we measure arrives in our comprehension through a large number of proxies, by proxy meaning an intermediary which is a mathematical function (necessary for physics observations) that deconvolutes the basic interaction (which is quantum mechanical) up to the level our brains can apprehend. Example: a basic proton antiproton proton annihilation seen in a bubble chamber. Ignoring that our eyes see it, the mathematical path is as follows: measure the curvature, deconvolute to momenta, masses, fit hypothesis to energy and momentum conservation, find total energy =mass of two protons. decide: proton antiproton annihilation. All these processes are classical but we arrive at a quantum mechanical measurement. In my opinion all measurements are classical but when deconvoluted to the quantum level measurement= registered interaction . What is the problem?