Note the contradiction in the following two sets of verses, discussing the requirement to allow the land to lie follow every 7th year (the so-called land sabbatical). Verse Lv25-20:23 states:
• And if you shall say, What shall we eat the seventh year? behold, we shall not sow, nor gather in our produce;
• Then I will command my blessing upon you in the sixth year, and it shall bring forth fruit for three years. And you shall sow the eighth year, and eat still of old fruit until the ninth year; until its fruits come in you shall eat of the old store.

We see the contradiction, indicated by the underlined phrases. Which is it? Are we prohibited from agriculture only in the 7th year? Or, are we also prohibited in the 6th and 8th year? If we are not prohibited in the 6th and 8th year why do we need a Biblical promise that the blessings of the sixth year will carry forward for three years.

It is not hard to resolve this contradiction. Rashi resolves it using some simple operational details:
• In each year we sow and harvest for that year and also the beginning of the next year. Hence, in the 6th year we sow and harvest (as usual) for that year.
• However the harvest from the sixth year, which should typically feed us for that sixth year, will also feed us for the totality of the 7th year when we can't perform agriculture.
• But then when the 8th year begins we still don't have any harvest. Rather we have to sow in the 8th year and we do not reap the harvest of the 8th year till after the summer. But after the summer is the Jewish New Year and the ninth year begins. Hence the harvest of the 6th year is needed while harvesting the agriculture of the 8th year which gets completed at the beginning of the 9th year.

Advanced Rashi: We have employed the contradiction method to explain the above verses. Further clarification may be obtained from the non-verse-diagram method. The following time diagram clarifies the above Rashi. Very often the use of two Rashi methods adds clarity. Please feel free to read rule #9, Spreadsheets-Diagrams now.