when people say 'it likes to draw a line in the sand', does it mean it is useless because the line is almost invisible? Or it means that the actions or things can't get any result?
I need more context to explain precisely-- what is 'it'? Meanwhile, to draw a line in the sand is an idiomatic phrase meaning to set a defined boundary for triggering a decision or an action. For example f my son continues to come home late every evening, I draw a line in the sand by telling him that if he comes home after 7 pm one more time, he gets no dinner!
I suggest to search for the meaning of the expression at Yahoo:

In this case a search with
"draw a line in the sand" dictionary
"draw a line in the sand" idiom
(quotation marks are important to group up terms)
would give you several pages describing the idiom

including this one
Word Detective by Evan Morris

The most recent use of the phrase "draw a line in the sand" was, of
course, by President George Bush at the beginning of the Gulf War. But
for the true clue as to the origin of the phrase, we turn to my
esteemed colleague William Safire, whom I especially esteem when he
does my work for me. In his book "In Love With Norma Loquendi" (a
collection of his Sunday New York Times Magazine columns, published by
Random House in 1994), Mr. Safire provides two possible origins for
"drawing a line in the sand."

The more recent possible origin for the phrase is an incident said to
have taken place during the siege of the Alamo in 1836, when William
Barret Travis drew a line in the sand with his sword and urged those
willing to stay and defend the fort to step across it. Unfortunately,
this heroic story seems to have been invented by a 19th century
promoter long after the fall of the Alamo. But the myth itself
probably greatly popularized the phrase, so it does count as an origin
of sorts even if the incident itself was apocryphal.