Nice to make your acquaintance Mark. I will try my best to help you here.
Immediately I notice that neither of these sentences are grammatically correct.
Errors in the Second Version:
The second version is actually even more erroneous than the first version. There are several causes for this, the first reason being your use of the word 'thing'. It is not proper English to use the word 'thing' because 'thing' does not refer to any subject in particular. 'Thing' can refer to 'thought', 'outcome' or even 'noodle'. You must provide context, otherwise your reader will not know what you are trying to refer to.
In other words, 'thing' is far too vague a word and you should always avoid its use. The idea is to express yourself as accurately as possible so that within the first reading of the sentence the receiver of the message you are attempting to communicate to understands exactly what you're attempting to convey.
You will never achieve this goal by using the word 'thing' because the reader does not know what you are referring to. Instead, you must replace the word 'thing' with the word 'effort'. Why? You do this because 'effort' is what you were referring to when you wrote 'thing', however only you know this and not your reader because, as aforementioned, 'thing' is vague and inaccurate. Accuracy is vital in order to convey your message.
Never use the word thing.
This is not the only error in this sentence, however.
Instead of 'The result starts with a very small thing, and very small thing becomes the most important', you could write:
The result starts with a very small effort, and this very small effort becomes the most important 'step in the process'.
What I have written in bold is an example. You can change it to suit your needs but unless you understand why my example is correct and your example is incorrect you will be unable to make the requisite amendments if you feel that they are needed.
The reason why the remainder of your example is grammatically incorrect is due to the sentence being incomplete. By merely writing 'The result starts with a very small effort, and this very small effort becomes the most important...', you are leaving the receiver wondering what the importance of this "very small effort" becomes, because you have failed to stipulate what it is.
Do you understand or do you need further elaboration?