Cat drinking beer is an unrestricted image from 12/1947. Bowery Follies downtown bar cat laps up a beer. This is a work of a U.S. Federal government employee. This photo is part of a person's official duties and is in public domain.
I thought this picture really went well with this entry because this is about the loss in brewing. After you've found out about brewing for the first time, you'll notice that beer brewing is really about getting the right taste. It is a balance between sweet and bitterness. If one over powers the other you have got a batch that is not quite right. Other people might say your brew is good because taste is in the taste buds of the drinker. What's good for one person may not be good for another. You might make a lot of interesting brews, but it is just like when you go to the store - try out a new beer and there is a 50/50 chance you'll like it.
When you make beer in the home you'll notice your first loss is getting the grains in the pot when you are ready to soak them in the pot. Grains scatter when you open a bag. Your next loss comes from not mashing your grains at the right temperature. The beginner might not control the temperature correctly and this creates a loss of taste. If you soak the grains at too hot a temperature you destroy the available sugar and possible alcohol in your batch. A little warmer than normal can give you sweet beer and less alcohol whereas lower temperatures might give you a dry beer with more alcohol. Your next loss is the sparge and lauter phase. This is pouring the hot water from pot to pot through a strainer holding your grains to get all the sugars off them as they will be discarded later. Some homebrewers use the brew in a bag method which is similar to the way I pour the hot liquid from one pot to another using the strainer. I don't use the method of a converted cooler made into a mash tun. (You can see these plans on the internet, but I don't like the idea of plastic leaching chemicals into my brew) I'm still trying to get the hang of pouring the liquid from one pot to the other. I've had my share of spills on the floor. Your next hurdle is to get your sparging water just right. If you sparge with too much water you'll end up with some of your hot liquid (called wort) not fitting in the carboy (your fermentation vessel). I'll cover the process later so this becomes more familiar. Homebrewing is still a science with some mystery as older breweries hold the secrets in their proprietary recipes. They know how to make great beer, but only some of the information is available to homebrewers in books. The boil is best done with the lowest heat to produce a boil. I have not discovered what really happens if you boil too high or low. Your next source of loss occurs at the fermentation stage. If you have not done a good job of cleaning and sanitizing your equipment some bacteria can bring a foul taste into your batch which will only be discovered later. Bad tasting batches may discourage beginning brewers at home. That beer kit that was a present at Christmas time may soon be tossed out after the first batch. As a beginner, you have to exercise persistence and discipline. This is just like every other activity or hobby. You won't become a master chef or professional race car driver over night. Your next lost can be from your spouse. You have to have a forgiving spouse because brewing beer can make a mess in the kitchen, create that brewery smell in the house for hours and fill up the sink with dirty pots or bottles. She might say, "I've had it with this brewing!" That might limit your brewing of some future recipes. The last source of loss is at the bottling stage. I've used plastic bottles from kits and leftover Grolsch bottles from the local party store. Both types of bottles work equally well, but I found I'm not really good at siphoning the beer from the glass carboy to the individual bottles. There is usually a loss of beer down the drain.
Well, I hope I haven't discouraged you from this hobby. Each hobby has its drawbacks. I find that this interest is a lot better than collecting stamps as I've done that as well. I think it is comparable to being a cook of a big holiday meal. If you enjoy that than that's fine. In the end, you'll have a nice bottle of beer as a reward for your efforts.