Blanks in Data Fields
Consider the following data step code and data values:

INPUT NAME :$25. AGE GENDER :$1.;  
DATALINES;  
RASPUTIN    45 M  
BETSY ROSS  62 F  
ROBERT LOUIS STEVENSON  75 M  
Proc Print;  
     Title 'Blanks in List Input';

List input uses blanks as field delimiters (one or more blank). Since there are single blanks within the names, the above code will not work.
Output

Blanks in List Input
  
OBS    NAME        AGE    GENDER
  
 1     RASPUTIN     45      M  
 2     BETSY         .      6  
 3     ROBERT        .      S

Log

27   DATA WontWork;  
28      INPUT NAME :$25. AGE GENDER :$1.;  
29   DATALINES;
  
NOTE: Invalid data for AGE in line 31 7-10.  
RULE:----+----1----+----2----+----3----+----4----+----5  
31   BETSY ROSS  62 F  
NAME=BETSY AGE=. GENDER=6 _ERROR_=1 _N_=2  
NOTE: Invalid data for AGE in line 32 8-12.  
32   ROBERT LOUIS STEVENSON  75 M  
NAME=ROBERT AGE=. GENDER=S _ERROR_=1 _N_=3  
NOTE: The data set WORK.WONTWORK has 3 observations and 3 variables.