With more and more records being indexed, it is tempting for some to quit searching when the index fails. Keep in mind that there are times where manual searching of a record is necessary. Indexes are not perfect and sometimes writing is extremely difficult to read.
The census is a good example. If you know where your ancestor lived and the index does not quickly locate him, search manually. If the relative was in a rural area, it may not take very long to page through a township or two in an attempt to find him. And in searching page by page, you may find other relatives in the process. In urban areas, you may be able to pinpoint your relative's location down to a handful of enumeration districts. And learning more about where your ancestor lived and tracking his residences may help you research more than just locating him in the census.
Those of us who researched in the days before census indexes relied on manual searches when we first started.