[General Questions and Answers] marth141:
Yeah, that is why you would want a custom recovery. However, having a custom recovery does not guarantee 100% brick protection. I'll explain what usually happens in your average "brick" event.

To understand this, you need to understand how Android works, which, this is the same with Linux and most other operating systems. When Android boots, the system immediately goes to the boot rom which immediately starts running the scripts and whatever else to begin the boot loader. The boot-loader then decides where it is you want to boot. If you're just starting your phone, it'll go to start the kernel, then the initializing scripts to run the system. If this is not where it goes, it'll go to run the scripts to run your recovery, or whatever other things it can run.

When we flash something, we're over-writing memory that is already on the phone forcibly. As you should well know, Android has a few partitions, /boot /system /recovery /data /cache and /misc. Boot, system, and recovery are considered Read-Only because they're the 3 most critical to making sure your phone works. /boot stores how the phone boots, loads the boot-loader, kernel, eventually leading us to go either into /system (your actual usable interface for SMS, phone calls, and facebook), or /recovery, where we can do maintenance. /data is where your apps and user data is stored. /cache is where a lot of system temporary files are stored and /misc is where a lot of system settings like region ID and what not is stored.

So. When we have a custom recovery, we are able to make images of most of these partitions. The recovery allows us to be able to flash these images onto the phone if for whatever reason one of them gets corrupted. From how I explained, you should be able to tell that /boot and /recovery then are two partitions that absolutely critical because /boot allows the phone to turn on and /recovery allows us to do maintenance if we mess something up by giving us the power to flash these images.

Now largely, if /boot or /recovery get messed up and if we take improper steps, we'll end up with a completely unusable phone. When flashing anything to /boot, which, usually you shouldn't have to, make sure that a new /boot image is actually on the phone (to the best of your ability) before you restart, otherwise, you aren't going to be able to fix this. If a bad recovery goes on, and prevents you from getting to recovery, depending on the phone, there may be some ways to get a recovery back on without needing to be in recovery. (You can't usually flash a recovery on while in recovery, so this one is fixable as well.)

So, learning from this, a very hard brick is when we have no /boot. At that point, we're pretty well ****ed and the phone is dead. Otherwise, with a custom recovery, it turns just about anything else that can happen into a soft brick.

Getting to the point: A custom recovery, as I said, is not a 100% protection against bricking your phone. However, it does allow us to fix just about anything that goes wrong with the phone via modding use. Root allows people to make changes to areas of the phone that we would otherwise not want changes to happen in. Some of these changes, depending on what you do, can result in a brick. This is because if a change was made in /system, and you try to factory reset using the standard recovery to fix it, android will delete the /data and /cache partitions and remake them based off /system. Which, at this point, you should understand that if /system is corrupt, that'll result in a non-workable phone. BUT, because we have our handy-dandy custom recovery, we can fix that. Because instead of just deleting the /data and /cache partitions, we'll just flash back on the old /system pre-changes. Which will result in a happy working android again.

That's why we want a custom recovery. Anyone who took the time to read this, please correct me where I'm wrong and clarify it.