Jimmy Song's blog lost me in the part when he starts explaining "Block Weight". Is there another way for someone to explain this "like I am 5"? I am not a very technical person but I really want to learn everything about Bitcoin.
Before, only one aspect of a transaction determined how large a block could be: it's size in bytes.
Now that Segwit is activated, there are two components: the size of the inputs + outputs, and the size of the signature. Inputs/outputs are the information that says "I'm paying this money from this address to that or those address/es". The signature is the part that proves you've got the right (i.e. the private keys) to pay.
Inputs & outputs can only use the 1MB of block space that Bitcoin previously had, they are "weighed" differently to signatures. Signatures are weighed at 1/4 of inputs & outputs (sometimes referred to as the "witness discount"), and so they can use a total maximum of 4MB of block space (but they've got to sign
some inputs, it's not possible for a block to contain only signatures signing nothing).
Typically, this will mean each block will be about 1MB of transactions and 1MB of signatures (because the average transaction is roughly one half input/output data and the other half signature data). That's means typically we'll have 2MB blocks (apparently it's more like 2.1MB). But increasing use of transactions with multi-sig (needed for Lightning and other future innovations) that increase average signature size will change the balance between in/outs and signatures, and blocks would get closer to using the 4MB total that is allowed.
