Security is not all or nothing. Locking doors and windows will keep out the laziest and lowest skilled thieves, but these are a substantial percentage of thieves who steal the easiest targets that they encounter. Additional security measures like better locks, alarms, etc. that can make the theft slower, noisier, or more difficult can screen out a larger percentage of thieves. It is true that keeping out the most skilled thieves is very difficult, but the most skilled thieves are only a small percentage of all thieves.
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