The brain fixes things on the fly.  To wit, you can probably read the following:

 

7H15                    M3554G3

53RV35                    7O PR0V3
H0W                    0UR M1ND5 C4N
D0                    4M4Z1NG 7H1NG5!
1MPR3551V3                    7H1NG5!
1N                    7H3 B3G1NN1NG
17                    WA5 H4RD BU7
N0W,                    0N 7H15 LIN3
Y0UR                    M1ND 1S
R34D1NG 17
4U70M471C4LLY
W17H                    0U7 3V3N
7H1NK1NG                    4B0U7 17,
B3  PROUD! 0NLY
C3R741N                    P30PL3 C4N
R3AD                    7H15.
PL3453                    F0RW4RD 1F
U                     C4N R34D 7H15.