[linest] Whu LINEST can't the precise parameter of each variable?

Here is my data:

x-y+z-1=0
x y z d
1 0.6 0.4 0.8
1.2 1.1 0.8 0.9
0.5 0.6 1 0.9
0.7 0.9 0.8 0.6

When I use LINEST as an array function like this:

=LINEST(C3:C6,A3:B6,,True)

The result I get is:

0.807365439 -0.8101983 0.792776204

Why I can NOT get precise parameter as -1,1,1?