The problems with drugs is that the brain seeks to compensate for whatever effect the drug is having, so when the drug eventually leaves our system the brain is then out of kilter. Imagine your brain as one of those memory foam mattresses. Flat is ok, a lump on it means you feel good, a dip means you feel bad. You put something on it to cause a lump (so you feel good) but the memory foam slowly dips under the weight of it. You take the object off, there is then an indentation or a dip (so you feel bad). The longer the object is there the more the memory foam dips under the weight of it, and the greater the depression (in both senses of the word) when the object is removed.
Another way of thinking about it is the pilings that run into the sea. Think of the pilings as your problems. The bigger the problem, the taller the piling. Think of the sea as your level of peacefulness, confidence, mental resilience, etc. Your brain can’t control the size of the problems (the pilings) but it can control the level of the sea.
You need to be aware of your problems, and to be motivated to do something about them, but you shouldn’t be so overwhelmed by them that you feel incapable of dealing with them, otherwise you’ll be frozen like a rabbit in the headlights of an oncoming vehicle. So your brain regulates the depth of the water such that the top of the pilings are just visible. It allows just enough of these pilings to be visible so that you are aware of them, but not so much as to scare you. Of course these problems can come and go, and suddenly you can have huge problems that arise that weren’t there a second ago. It takes time to change the level of the sea, but leave it long enough and it will slowly seek that same level where just the top of the pilings are visible.
When you drink alcohol you are artificially raising the level of the sea. In the short term it’s fine, you can completely cover the pilings (your problems). But the problem with doing this is that your brain doesn’t want the pilings covered otherwise you have no motivation to tackle your problems. So it starts to lower the level of the sea. At the same time the alcohol wears off, with the result that the sea level drops far too low, exposing not just the top of the pilings, but virtually all of it. The problem that was originally just an irritant now looks insurmountable. Now you desperately need more alcohol to raise the sea level to make your problems seem manageable.
In fact the pilings analogy is an extremely good one. Firstly it shows how you can have a problem, but if a bigger problem comes along the previous lessor problem is soon forgotten. The water level acclimatises to the height of the largest pilling, and shorter ones are submerged. Secondly it shows how even huge problems eventually become part of the background noise of our lives, no longer dominating our every thought. Imagine being thrown into prison, imagine how scared and miserable you’d be. But if you were in prison for years you’d have good times as well as bad. You’d laugh, you’d enjoy certain meals, certain books, certain tv shows or recreational activities. I’ve never been in prison but I have spent 6 months serving in Iraq. There was a constant threat of attack even in camp (being woken up in the middle of the night in the supposed safety of the camp by a mortar attack is one the most vivid memories of my life). It was hot, dusty, dangerous, and very hard work. But there were still good times. A full 8 hours of unbroken down time, a shower, a decent meal. Yet 12 years down the line I have recently become extremely irate because of problems with our home broadband. I didn’t even have broadband in Iraq, it never once bothered me.
We acclimatise to what we have, good or bad. If you have everything you want you will still find something you want to improve. That is human nature, a natural and healthy desire to improve our lot, and the lot of our loved ones. Conversely no matter how bad things get, over time you will always find something to be glad or thankful for. That is the way our brains work, how we deal with problems without drowning in them, how we can find things to enjoy in life no matter how bad things get.
When you are regularly anaesthetising yourself with alcohol you rob yourself of that. You never allow yourself to acclimatise to the bad because you are always anesthetising it, or to go back to the pilings analogy, you never allow the sea to find its optimum level which is the perfect balance between caring, but not caring too much. When you are drinking you are constantly yo-yoing between being utterly overwhelmed by your problems and not caring about them in the least.
Either way you end up doing absolutely nothing about them.