The same thing is true of our spiritual lives. We come in contact with temptations every day, but when we are strong and healthy from a good diet of God's Word and have exercised ourselves unto godliness and are spending time in quiet rest and meditation and prayer we can face many temptations every day without becoming infected with sin. Unfortunately, we are sometimes under nourished or overwhelmed with activities that look good and may be good, but which overtax us spiritually and don't leave us with the time we need to work on our relationship with the Lord. When those things happen, we can easily be attacked by Satan.
It is interesting to notice that sometimes our spiritual health will affect our physical health, and sometimes our physical health can affect our spiritual health. What causes your spiritual infections? How do you fight them off?